Currently the library reports on:
- Lines of code: Both physical (the number of lines in a module or function) and logical (a count of the imperative statements). A crude measure.
- Number of parameters:
Analysed statically
from the function signature,
so no accounting is made
for functions that rely on the
argumentsobject. Lower is better. - Cyclomatic complexity: Defined by Thomas J. McCabe in 1976, this is a count of the number of cycles in the program flow control graph. Effectively the number of distinct paths through a block of code. Lower is better.
- Cyclomatic complexity density: Proposed as a modification to cyclomatic complexity by Geoffrey K. Gill and Chris F. Kemerer in 1991, this metric simply re-expresses it as a percentage of the logical lines of code. Lower is better.
- Halstead metrics: Defined by Maurice Halstead in 1977, these metrics are calculated from the numbers of operators and operands in each function. Lower is better.
- Maintainability index: Defined by Paul Oman & Jack Hagemeister in 1991, this is a logarithmic scale from negative infinity to 171, calculated from the logical lines of code, the cyclomatix complexity and the Halstead effort. Higher is better.
- Dependencies:
A count of the calls
to CommonJS and AMD
require. Analysed statically from the function signature, so no accounting is made for dynamic calls where a variable or function is obscuring the nature of the dependency. Lower is better. - First-order density: The percentage of all possible internal dependencies that are actually realised in the project. Lower is better.
- Change cost: The percentage of modules affected, on average, when one module in the project is changed. Lower is better.
- Core size: The percentage of modules that are both widely depended on and themselves depend on other modules. Lower is better.
It is important to note that none of these metrics can compete with the insight of a competent developer. At best, they are an automatable warning system, which can help to identify areas of code that warrant closer inspection by a human being.
- A Complexity Measure, by Thomas J McCabe.
- Cyclomatic Complexity Density and Software Maintenance Productivity, by Geoffrey K. Gill and Chris F. Kemerer.
- Resolving the Mysteries of the Halstead Measures, by Horst Zuse.
- Exploring the Structure of Complex Software Designs: An Empirical Study of Open Source and Proprietary Code, by Alan MacCormack, John Rusnak and Carliss Baldwin.
- The Impact of Software Design Structure on Product Maintenance Costs and Measurement of Economic Benefits of Product Redesign, by Andrei Akaikine.
- Think Twice Before Using the “Maintainability Index” by Arie van Deursen.
- A Systematic Review of Software Maintainability Prediction and Metrics, by Mehwish Riaz, Emilia Mendes and Ewan Tempero.